The present invention relates to devices for directing a beam of coherent radiation at a target and, more particularly, to a fiber-laser-based device for neutralizing unexploded ordinance and for similar applications.
Laser-based systems for neutralizing unexploded ordinance are known. One such system is the ZEUS™ system produced by the International Systems Operation division of Sparta Inc., located in Huntsville, Ala., USA. FIG. 1 is a partial high-level schematic diagram of such a system 10. A continuous wave laser 12, a telescope 16 and a video camera 18 are mounted on a gimbaled platform 14. These four components are controlled by an operator using a fire control console 20. The operator uses video camera 18 to locate a target to be neutralized. More specifically, the operator turns and tilts platform 14 until the target is centered in a video screen in fire control console 20 that displays the images acquired by video camera 18. Video camera 18 is boresighted to laser 12 and telescope 16 so that when the target is centered in the video screen, laser 12 and telescope 16 are aimed at the target and a beam 22 of coherent radiation that is emitted by laser 12 when laser 12 is activated and that is focused by telescope 16 strikes the target. The operator focuses telescope 16 on the target and activates laser 12 to generate coherent beam 22. The operator continues to monitor the target using video camera 18 to verify that coherent beam 22 has indeed neutralized the target.
It would be advantageous to position laser 12 remotely from platform 14. The advantages of such a system include that platform 14 could be made lighter and/or mechanically more stable if platform 14 does not need to bear the weight of laser 12, and that a kinetic weapon such as a light or heavy machine gun could be mounted on platform 14 to supplement coherent beam 22 without the vibration of the kinetic weapon interfering with the operation of laser 12. An optical fiber would be used to convey coherent beam 22 from laser 12 to telescope 16.
Heretofore, two problems have prevented the implementation of such a system. Both problems are related to the high power of coherent beam 22 that is needed to neutralize the intended targets.
The first problem relates to the coupling of a conventional laser 12 (for example the Nd:YAG laser used in the Zeus system) to the optical fiber. To produce an adequately bright coherent beam 22 with a small spot size on the target, the combination of laser 12 and the optical fiber should have a low “beam parameter product” (BPP). To have a sufficiently low BPP, the optical fiber should have a narrow-diameter core. It is difficult to optically couple the high-power coherent beam 22 generated by laser 12 to a sufficiently narrow core without damaging the optical fiber.
The second problem is that the high power of coherent beam 22 gives rise to nonlinear effects such as Stimulated Raman Scattering and Stimulated Brillouin Scattering in the optical fiber. These nonlinear effects reduce the power of the coherent beam that finally emerges from the optical fiber and so limit the length of the optical fiber that can be used to couple laser 12 to telescope 16.